/*
 * Copyright 2020  Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.grpcweb;

import com.google.common.annotations.VisibleForTesting;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.http.HttpServletRequest;

class MessageHandler {
  @VisibleForTesting
  enum ContentType {
    GRPC_WEB_BINARY,
    GRPC_WEB_TEXT;
  }

  private static Map<String, ContentType> GRPC_GCP_CONTENT_TYPES =
     new HashMap<String, ContentType>() {{
         put("application/grpc-web", ContentType.GRPC_WEB_BINARY);
         put("application/grpc-web+proto", ContentType.GRPC_WEB_BINARY);
         put("application/grpc-web-text", ContentType.GRPC_WEB_TEXT);
         put("application/grpc-web-text+proto", ContentType.GRPC_WEB_TEXT);
     }};

  /**
   * Validate the content-type
   */
  ContentType validateContentType(HttpServletRequest req) throws IllegalArgumentException {
    String contentType = req.getContentType();
    if (contentType == null || !GRPC_GCP_CONTENT_TYPES.containsKey(contentType)) {
      throw new IllegalArgumentException("This content type is not used for grpc-web: "
          + contentType);
    }
    return getContentType(contentType);
  }

  static ContentType getContentType(String type) {
    return GRPC_GCP_CONTENT_TYPES.get(type);
  }

  /**
   * Find the input arg protobuf class for the given rpc-method.
   * Convert the given bytes to the input protobuf. return that.
   */
  Object getInputProtobufObj(Method rpcMethod, byte[] in) {
    Class[] inputArgs = rpcMethod.getParameterTypes();
    Class inputArgClass = inputArgs[0];

    // use the inputArg classtype to create a protobuf object
    Method parseFromObj;
    try {
      parseFromObj = inputArgClass.getMethod("parseFrom", byte[].class);
    } catch (NoSuchMethodException e) {
      throw new IllegalArgumentException("Couldn't find method in 'parseFrom' in "
          + inputArgClass.getName());
    }

    Object inputObj;
    try {
      inputObj = parseFromObj.invoke(null, in);
    } catch (InvocationTargetException | IllegalAccessException e) {
      throw new IllegalArgumentException(e);
    }

    if (inputObj == null || !inputArgClass.isInstance(inputObj)) {
      throw new IllegalArgumentException(
          "Input obj is **not** instance of the correct input class type");
    }
    return inputObj;
  }
}
